1. Field of the Invention
The present invention relates to controlling the amplification of signals transmitted by mobile radiocommunication terminals, especially when using heterojunction bipolar transistor power amplifiers.
2. Description of the Prior Art
To provide sufficient power during the sending phase, the signal sent by a terminal such a mobile telephone must be amplified.
To this end terminals include a power amplifier receiving an input power and delivering an amplified output power, the amplification depending on a control voltage fed to the amplifier.
Some power amplifiers using the heterojunction bipolar transistor (HBT) technology are more efficient and much smaller than power amplifiers using other technologies.
In some cases the transmission architecture adopted by mobile terminal manufacturers is a zero intermediate frequency architecture. In this type of architecture, which reduces cost and size, the amplitude conversion related to amplification (referred to as AM/AM conversion) is a very important parameter. Spectrum degradation associated with AM/AM conversion is critical in a zero intermediate frequency architecture.
The degradation is very high at low amplifier output powers in a power amplifier using heterojunction bipolar transistors because the amplifier receives high input powers.
This being so, an object of the present invention is to palliate these drawbacks by proposing a method and a circuit enabling use of a power amplifier using heterojunction bipolar transistors in a zero intermediate frequency transmission architecture that reduces observable spectrum degradation.